Hand-held lawn and garden tools, such as string or blade trimmers, are well known in the art and are used in many applications to cut vegetation in places that are typically inaccessible to conventional lawn mowers. Standard string trimmers include a cutting mechanism having a rotating head from which a flexible string or cutting line protrudes, a handle having a trigger that enables an operator to actuate the cutting mechanism and a shaft connected between the cutting mechanism and the handle that allows the operator to move or swing the cutting mechanism from a standing position.
Some known lawn and garden tools, such as string trimmers, include a shaft that may be extended or retracted to change the length of the device to thereby accommodate users of different heights. Also, some known string trimmers include a shaft that may be rotated by 180 degrees or more with respect to a handle of the trimmer to allow the cutting mechanism to be oriented in either a horizontal plane or in a vertical plane, which is common in edging applications. Some string trimmers have a shaft capable of both rotation and elongation, but typically include a complex shaft adjustment mechanism that is difficult to operate and/or that is located at an inconvenient place on the device.
For example, Brant et al. (U.S. Pat. No. 5,594,990) discloses a string trimmer having a shaft that may be initially elongated to a predetermined length and that may be rotated by 180 degrees at any time during operation. The Brant et al. trimmer includes a shaft having spring-loaded pins that protrude from the sides thereof and that are moveable in a radial direction with respect to the shaft. When the string trimmer is first removed from the box, the pins are disposed in axial channels formed within a casing of the cutting mechanism of the trimmer. The axial channels terminate at a pair of circumferential channels. During initial set-up, the shaft is elongated by pulling on the shaft, which forces the pins to slide within the axial channels toward the circumferential channels. Ramps disposed at the ends of the axial channels force the pins radially inwardly as they approach the circumferential channels and, when the ends of the axial channels are reached, the pins snap radially outwardly into the circumferential channels where one of the pins is locked into place. At this time, the pins are prevented from returning to the axial channels by the walls of the circumferential channels, thereby preventing further axial movement of the shaft.
During operation, a button on the casing of the cutting mechanism of the Brant et al. trimmer may be actuated to force the locked pin radially inwardly, out of the locking position. This movement enables the pins to travel 180 degrees within the circumferential channels, thereby allowing the shaft to rotate with respect to the casing until the other pin reaches a locking position. In this manner, the string trimmer can be reconfigured from a horizontal cutting device to a vertical cutting device or vice-versa. Unfortunately, the shaft of the Brant et al. device cannot be elongated or shortened after initial set-up and cannot be locked at an axial position other than the predetermined position associated with the circumferential channels. Also, the button of the Brant et al. device (which enables rotation of the shaft) is located on the casing of the cutting mechanism, which is inconvenient because it forces the user to bend over to effect rotation of the shaft or the cutting mechanism.
European Patent Application Number 0 653 364 A2 discloses a string trimmer having a shaft that may be elongated and/or rotated. The string trimmer of this document includes a square shaft with a series of serrations disposed on each of the four sides thereof, a locking mechanism having four teeth adapted to be disposed within one of the serrations on each of the four sides of the shaft and a locking ring that rotates between a first position, at which the teeth are locked within the serrations, and a second position at which the teeth are removable from the serrations. In order to elongate or rotate the shaft, the locking ring is rotated to the second position so that the teeth are allowed to come out of the serrations of the shaft. Thereafter, the shaft may be rotated and/or elongated until the teeth reside in different ones of the serrations. When the desired rotation or length of the shaft has been attained, the locking mechanism is rotated back to the first position, which locks the teeth within the serrations to prevent movement of the shaft with respect to an upper housing of the string trimmer.
While the string trimmer disclosed in this document allows telescoping and rotation of a shaft, the locking mechanism is difficult to actuate because it requires a user to grasp and then to rotate a member around the shaft of the string trimmer. Likewise, the locking mechanism is not positioned at an easily accessible place on the handle of the string trimmer but is, instead, located between the upper housing and the cutting mechanism, which again forces the user to bend over to actuate the locking mechanism.